This disclosure relates generally to cooling within a gas turbine engine and, more particularly, to cooling leading edges of components aft of variable vanes.
Gas turbine engines are known and, typically, include a fan delivering air into a bypass duct as propulsion air and to be utilized to cool components. The fan also delivers air into a core engine where it is compressed in a compressor. The compressed air is then delivered into a combustion section where it is mixed with fuel and ignited. Products of the combustion pass downstream over turbine rotors, driving them to rotate.
Some portions of the gas turbine engine can include variable vanes. As known, adjusting the variable vanes alters flow through the gas turbine engine and can improve overall engine performance. Adjusting variable vanes alters flow to the blades aft the variable vanes, which changes the position and characteristic shape of the stagnation point along the surface. This changes the areas of the blades having the highest heat transfer coefficients.
More specifically, actuation of the variable vanes alters the inlet angle to the downstream blades can alter the stagnation location from positive incidence (pressure side stagnation location), neutral incidence (leading edge stagnation location), to negative incidence (suction side stagnation location). The heat transfer coefficients located at a stagnation point of the flow over blades downstream the variable vanes can be 1.5 to 2 times greater than the heat transfer coefficients on the other portions of the blade surface. Thus, aside from aerodynamic ramifications of this change in stagnation location, cooling the blades downstream of variable vanes becomes problematic, especially at the leading edge.